Calis



March 13, 1956 M. CALIS 2,738,284

CERAMIC DIELECTRIC AND PROCESS OF PREPARING IT Filed May 6, 1954 1N VENTOR M/CHE L INE CAL /8 BY X411 (3.

AGENTS new" A.

United States Patent Generale de Telegraphie Sans Fil, a corporation of France Application May 6, 1954, Serial No. 428,033 Claims priority, application France May 7, 1953 zClaims. (Cl. 106-39) The present invention relates to ceramic dielectrics of low power factor, suitable for electric capacitors of high quality intended for radio-electric apparatus of high frequency.

The invention relates more specifically to ceramic dielectrics presenting a high dielectric constant, low power factor, high insulating resistance, high dielectric strength, and temperature coeflicient substantially equal to zero.

Ceramic dielectrics are known which have a low power factor of about 2.10- at l megacycle. The principal component of such dielectrics is either a silicate of magnesium (steatite), the dielectric constant of which is approximately 6 and the temperature coefiicient of which is slightly positive (of the order of +100.l0 or titanium oxide, the dielectric constant of which is approximately 80 and the temperature coeificient of which is negative (of the order of -850.10 By suitable proportions of the components, it is possible to attain any temperature coefiicient in the range between that of steatite and that of titanium oxide (from +100.10- to -850.l0 included zero). To each value of the temperature coefficient there corresponds a value of dielectric constant and there is substantially a linear law between the two limiting values above mentioned. Moreover a composition is known which has a dielectric constant in the neighborhood of 200 with a temperature coeflicient that is very low, only within narrow temperature limits of about +10 to +50 C. In general that temperature interval is insuificient to meet the specifications of capacitor manufacturers.

Ceramic dielectrics with zero temperature coelficient can be reproduced only with difficulty. On the one hand, a slight change in the dielectric formula (which may occur in case of a slight error of weight of one of the components) results in wide variation in temperature coeflicient. On the other hand the baking temperature has a great influence upon the value of the temperature coeflicient for compositions of the type wherein a slight change of the composition (we are concerned with the final composition as determined by X-ray analysis, which depends at the same time upon the weight of oxides in the paste composition, the baking temperature, the atmosphere in the oven, etc.), brings about a wide variation in temperature coefficient. Accordingly, it is very diflicult to attain an accurately predetermined temperature coeificient with such compositions.

An object of the present invention is a ceramic composition which, in the absence of special precautions and with the use of inexpensive ovens, permits the attainment of a temperature coeflicient accurately maintained with low tolerances at the value zero.

According to the invention the ceramic paste has the following composition:

2,738,284 Patented: Mar. 13, 1956 The following description and the accompanying drawing given byway of non-limitativ'e example, Will assist in understanding the invention.

The drawing shows the variation of dielectric temperature coefficient K6, as a function of the percentage of the S1102 component, of a product according to the invention. It is seen that, when the amount of S1102 is varied from 11 to 15 per cent, the temperature coeificient remains substantially zero.

The range of composition above referred to comprises l imits sufiiciently wide to meet extreme conditions. Most satisfactory results are obtained with the following range of proportions:

Grams TiOz 45 Z102 37 BaO 6.6 ZnO 3.6 SnOz 13 Clay 10 The manufacture of the ceramic product in question.

is eflected by well known procedure. The components are weighed and crushed to fine powder. The components are mixed for example in a ball mill, the bowl and balls of which are of porcelain. The powdered mix thus obtained is converted into a paste by adding an organic binder. The dielectric pieces are formed from the paste by any known procedure, as for example, by molding or extrusion. The pieces thus obtained are subjected to baking at a temperature between 1200 and 1350 C. If it is desired to regulate the contraction of the pieces, the mix may be subjected to a preliminary baking operation at a temperature between 1100 and l300 C. After such preliminary baking, the mass is crushed again and reduced to a fine powder. The powder thus prepared may then be treated according to the procedure previously described. There could, if desired, be added to the prebaked powder, powder of the same composition which had not been prebaked.

The dielectric losses of ceramic thus made are less than 2.10' at 1 megahertz, the temperature coefficient is Zero with a variation of less than about 110.10 and the dielectric constant is between 20 and 30.

Of course, instead of the oxides TiOz, ZrOz, BaO, ZnO, SnOz, there may be used the corresponding carbonates as raw components in the process of making said ceramic dielectrics. For instance, there may be used 9 to 7 grams of BaCOa instead of 7 to 5 .5 grams of BaG. After baking, only BaO is found in the finished product.

The mineral elements of the compositions according to the present invention may easily be determined in practice by diffraction analysis. Manifestly chemical analysis admits of checking the proportions of these elements in the finished product to assure that they are substantially identical to the composition of the paste, bearing in mind the elimination in the course of baking, of CO2 from carbonate components such as BaCOs. Consequently the composition of the product may readily be ascertained from that of the paste and conversely.

As many changes could be made in the above composition and many apparently widely difierent embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, What I claim as new and desire to secure by Letters Patents of the United States is:

1. Ceramic dielectric product consisting essentially of:

Grams TiOz 34 to 45 ZrOz 40 to 27 BaO 7 to 5.5 ZnO 4 to 3.4 SnOz 10 to 15 Aluminum silicate 12 to 18 4 2. Ceramic dielectric product consisting essentially of: Grams TiO2 45 ZrOz 37 BaO 6.6 ZnO 3.6 S1102 13 Clay 10 References Cited inthe file of this patent UNITED STATES PATENTS 2,643,192 Jonker et al June 23, 1953 FOREIGN PATENTS 282,198 Switzerland 1952 

1. CERAMIC DIELECTIRC PRODUCT CONSISTING ESSENTIALLY OF: 